The present invention relates to a method for imparting an aroma to foodstuffs, which aroma is generally associated with (freshly) fried onion and similar species.
Onions and other members (e.g. garlic, leek, shallots, chives, etcetera) of the botanical genus of Allium are well known ingredients in dishes around the world. These ingredients are capable of imparting a distinct taste and aroma to foodstuffs. When freshly preparing foodstuffs in which the aroma and taste of onions is desired, this will generally involve cutting or chopping onions which are then fried or sauteed for several minutes, usually in oil or butter. In particular the taste and aroma of freshly fried or sauteed onions is liked in e.g. soups and sauces.
In the ever increasing range of convenience food, which is partly or fully cooked, the taste and aroma of fried onions is in many cases a desired attribute. The industrial manufacturer may achieve this by incorporating fried onions in the foodstuff at some stage in the industrial process. Such fried onions may be either freshly prepared, dried or frozen or otherwise processed. Although this may provide acceptable results with respect to taste, the general experience is that a so-prepared foodstuff will in most cases lack the agreeable aroma of freshly fried or sauteed onions, which the housewife will perceive when freshly preparing a dish with onions which are fried or sauteed during the preparation of the dish.
When incorporating fried onions (whether it be dried, frozen, or freshly prepared and further processed for obtaining keepability) in a fully or partly prepared foodstuff, the distinct aroma of fried onions is apparently lost at some stage during processing to such an extent that when the consumer opens the packaging of said foodstuff and heats or finishes the preparation prior to consumption, there is little to no aroma perceived of fried onions.
Although the taste may be improved by incorporating in said foodstuffs a xe2x80x9cfried onionxe2x80x9d flavour as supplied by various flavour manufacturers, the results in terms of fried onion aroma are still disappointing in many respects.
Various references in the past have attempted to shed some light on the complex chemistry and composition of fried onion flavour. Among such references are: E. Block, Angew. Chem. Int. Engl., 31, 1135-1178 (1992), E. Block and S. H. Zhao, Tetrahedron Letters, 31(35), 4999-5002 (1990), E. Block and E. M. Calvey, Sulfur Compounds in Foods, 63-79 (1994).
Following the above, there is a need for a convenient method for imparting a (fresh) fried onion aroma or odour to a foodstuff. Preferably, this objective should be achieved for (but not limited to) pre-processed foodstuffs such as convenience food, which only needs to be heated (with or without the addition of water) by the consumer. Examples of such foodstuffs are e.g. soup- and sauce base products (for example in dry form).
It has now been found that the above may be achieved by a method for imparting a (fried) onion aroma and/or odour to a foodstuff, wherein cis/trans-3,4-dimethyl-2-mercapto-2,3-dihydrothiophene (DMMT) is added to said foodstuff, with the proviso that this is not achieved by adding species of plants or (processed) parts thereof belonging to the genus of Allium. Preferably, DMMT is added to the foodstuff in an amount of 1 to 1000 ppm, more preferably 50 ppb to 50 ppm, preferably 250 ppb tp 5 ppm. For some purposes, an upper limit of 1000 ppb may be preferred.
Alternatively, DMMT may be applied next to the presence of plants or (processed) parts thereof belonging to the genus of Allium, in a method for imparting a (fried) onion aroma and/or odour to a foodstuff, wherein cis/trans-3,4-dimethyl-2-mercapto-2,3-dihydrothiophene (DMMT) is added to said foodstuff in an amount of at least 50 ppb, and less than 1000 ppm. For some purposes, depending e.g. upon the foodstuff to which DMMT is applied such amounts may be different, e.g. amounts of at least 150 ppb, preferably at least 250 ppb and less than 1000 ppm may be preferred.
The compound cis/trans-3,4-dimethyl-2-mercapto-2,3-dihydrothiophene (DMMT) has a structure as is set out in FIG. 1. 
This compound is not present in raw onions, but is formed (together with an abundance of other odourants, flavourants, aroma- or taste compounds) by the subsequent action of cutting or comminuting onions, frying the so obtained pieces in fat or oil (or any alternative heat treatment in the presence of triglycerides like sauteeing, simmering or deep-frying). It is thought that both the cis and the trans-form of DMMT provide a fried onion aroma, although one may have a stronger effect than the other.
DMMT can be prepared according to the various references by E. Block, as reported herein.
In an alternative way, instead of or in addition to adding DMMT to foodstuffs a precursor of DMMT may be added to the foodstuff, which precursor may be converted to DMMT e.g. upon the application of heat. Such a precursor is di(1-propenyl)disulfide (FIG. 2). This compound can be converted into DMMT easily by application of heat, typically 90-120xc2x0 C.) for 1-15 minutes. Heating to perform such conversion is preferably carried out in oil, such as when frying meat, fish or vegetables.
Hence, the invention relates to a method for providing a foodstuff which, when heated, displays a (fried) onion aroma and/or odour, wherein di(1-propenyl)disulfide (DPDS) is added to said foodstuff, with the proviso that this is not achieved by adding species of plants or (processed) parts thereof belonging to the genus of Allium. DPDS is a precursor of DMMT, and can be converted in DMMT by applying suitable heat (e.g. conditions as are present when frying meat or vegetables). The amounts in which DPDS can suitably be applied are similar to that of DMMT. DPDS and DMMT may be applied in a composition jointly or separately.
Likewise, the invention further relates to a method for providing a foodstuff which, when heated, displays a (fried) onion aroma and/or odour, wherein di(1-propenyl)disulfide (DPDS) is added to said foodstuff in an amount of at least 50 ppb, preferably at least 250 ppb, and less than 1000 ppm.
The advantage of using the precursor is that some time and heat is needed to form most of the aroma. Especially when a combination of DMMT and the precursor is used in the preparation of a packed foodstuff, this may result in a packed foodstuff which liberates a fried onion aroma when the pack is opened (DMMT) and when the product is heated sufficiently, more DMMT is liberated as it is formed in situ following the conversion of the precursor (e.g. di(1-propenyl)disulfide) into DMMT. As the precursor is also present in the process of actually frying onions, no off-flavours or other disturbing components are introduced.
As DMMT is not very stable in the presence of water, the method according to the invention is preferably applied to foodstuffs which have a low to very low water content (awless than 0.7, preferably less than 0.5). Examples of such foodstuffs are dry mixes (e.g. packed in sachets) for preparing soup or sauce, which can be turned in a soup or sauce by administering water or other aqueous liquid and optionally applying heat. The threshold value and volatility of DMMT are such that when DMMT is incorporated by the manufacturer of a dry soup or sauce in the dry mix, the aroma of freshly fried onions is almost immediately noticed once the packaging (e.g. a sachet) is opened. This will contribute to a positive, freshness appeal of the foodproduct, which is of particular importance in the case of dry mixes for soups and sauces, e.g. tomato-based sauce and soup. The aroma will be noticeable until some time after opening the packaging (i.e.during preparation).
The water content in such compositions will usually be low (aw less than 0.7, preferably less than 0.5). Particulate composition having such water activities are preferred. A low level of water present will enhance stability of DMMT. However, application is not limited to dry foodstuffs. When a certain amount of water is present, measures will have to be taken to prevent DMMT from degrading. This can be done e.g. by encapsulating DMMT or by the addition of antioxidants.
The method according to the invention is preferably applied to foodstuffs which are ambient stable, or which are processed such that they become ambient stable. Examples of ambient stable foodstuffs to which the method according to the invention may be applied are e.g. frying oils, frying fats and mixtures of such oils and fats. Other foodstuffs include for example mixtures of oils and/or fats with herbs and/or spices added thereto, as become increasingly popular in e.g. stir-fry dishes. Usually, such mixtures have very limited amounst of water in them, which make them very suitable for addition of DMMT and/or DPDS according to the invention.
Suitable amounts for adding DMMT and di(1-propenyl) disulfide to the foodstuff are 1 to 1000 ppb, preferably 10-100 ppb, based on the total weight of the packed product.
The invention further relates to compositions obtained following the method(s) as set out above, such as edible compositions comprising at least 50 ppb, preferably at least 250 ppb and less than 1000 ppm, of di(1-propenyl) disulfide (DPDS), and/or at least 50 ppb, preferably at least 250 ppb, and less than 1000 ppm of cis/trans-3,4-dimethyl-2-mercapto-2,3-dihydrothiophene (DMMT). Such edible compositions may further comprise at least 20%, preferably at least 40% by weight of edible fat, oil, or mixtures thereof. Examples of such compositions are e.g. frying oil, frying fat, or mixture thereof, optionally further containing herbs and spices.
Alternatively, the composition as set out above is a soup or sauce base product, which may be turned into a soup or sauce by dillution with an aqueous liquid, optionally under the application of heat.
For some purposes, it may be desired to have DMMT and/or DPDS are present in the composition predominantly in an encapsulated form.
As the precursor of DMMT (i.e. di(1-propenyl)disulfide) is in good rates transferred into DMMT when frying in oil, the invention also extends to oil or fat containing at least 1 ppb of di(1-propenyl)disulfide, preferably at least 10 ppb, and less than 1000 ppm. Preferably, this is achieved in the absence of plants or (processed) parts thereof belonging to the genus of Allium.